You could use an IDR, but it go off from other souces of light. An IR detector will only sense IR which is given off by a flame. I'm not sure exactly what frequencies a flame gives of, but I don't think that wouldn't be to hard to find.

Logged

"God chose to make the world according to very beautiful mathematics."-Paul Dirac**************************************************************Its Hawaii Five-O. Get it?

How do I make a small sensor [...] when it detects too much light it sets an alarm off?

Many fire alarm systems include thermal detectors, as a quite effective means of detecting fire.I don't know exactly what fire you wanna detect, the ones under the pot or those that may arise from forgetting your stew for too long (Which may sometimes only result in a glowing mass and black smoke).In each case, a thermocouple bead could be a viable solution, as in any case, the temperature will rise rather quickly in case of a fire. Further, Thermocouple beads come in variants that easily cope with 1300°C.

Logged

Regards,Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?Please remember...Engineering is based on numbers - not adjectives

HI,i made a fire sensor for fire fighting robot competition which won both 1st and 2nd places.I used a simple IR detector(one like 2SD400 transistor bt only with 2 pins) and a differential amplifier.it works very well.only draw back is its sensitivity greatly reduces with sun light.